This invention relates generally to a system for forming and welding a wire cage useful in reinforcing standard concrete pipe, and more specifically to a method and apparatus for automatically forming and welding wire cages from prefabricated wire mesh at high production rates with welds that are consistent and of high quality even though the wire mesh may be somewhat rusted.
In manufacturing standard concrete pipe it is standard practice to reinforce the concrete pipe by molding the concrete around a preformed wire mesh cage. Most commonly, the cages are formed manually by cutting a length of mesh from a prefabricated wire mesh coil and then welding opposite ends of the cut length through the use of a hand operated electric arc resistance welder. In addition to being very slow, forming and welding the cages by hand fails to produce cages of uniform size and quality, particularly when the prefabricated wire mesh is somewhat rusty and dirty as it often is from sitting around at the manufacturing plant. The rust and dirt often interferes with the arc resistance welding process and causes difficulty in securing high quality welds as required by standard ASTM specifications. Consequently either the welds ultimately provided are inferior or a great deal of time is required to scrape and clean the wires before welding.
In the past, systems have been proposed to form and weld wire cages as illustrated by the apparatus disclosed in prior U.S. Pat. Nos. 3,370,150, 3,678,971, 3,939,879 and 4,160,146. None of the systems however have been widely accepted within the industry either because of cost, unsatisfactory performance, complicated construction and/or maintenance, and particularly because of their inability to work with wire mesh which may be contaminated with rust or dirt. All of the systems disclosed by those prior patents utilize the electric arc resistance welding method which is directly adversely affected by the presence of rust on the mesh being welded. Consequently for the most part the hand forming and welding operation remains the predominant method within the industry.